CD4+CD25+ Treg cells regulate microglia and provide neuroprotection in ALS Amyotrophic lateral sclerosis (ALS), the most common motor neuron disease, is characterized by the extensive loss of motoneurons in the brain and spinal cord. The cause of ALS is unknown, and there is no known cure. Neuroinflammation, characterized by activated microglia and infiltrating immune cells, is a pathological hallmark in both ALS patients and ALS mice. Current evidence suggests that microglial/macrophage activation may be a double-edged sword. Numerous studies have concluded that alternatively activated macrophages (M2) are protective, while classically activated macrophages (M1) are toxic. The M1/M2 macrophages phenotypes have been shown to be modulated by CD4+ T-cells, especially CD4+CD25+ T regulatory (Treg) cells. However, little is known about the interaction between microglia/monocyte activation states and CD4+CD25+ Treg cells in ALS. Our preliminary studies with mSOD1G93A mice demonstrated that microglia may exhibit an M2 phenotype at early phase when disease was slowly progressing and an M1 phenotype at end stage when disease was rapidly progressing. Our in vivo data showed that the absence of CD4+ T-cells accelerates disease progression of mSOD1 mice. In the spinal cords of mSOD1G93A/CD4-/- mice, expression of an M2 marker, Ym1, as well as neurotrophic factors were decreased, while inflammatory factors were significantly increased. We determined that mSOD1G93A CD4+CD25+ Treg cells inhibited activation of adult mSOD1G93A microglia, as measured by NOX2 expression, when compared with mSOD1G93A CD4+CD25- T- cells. Moreover, CD4+CD25+Foxp3+ Treg cells expanded during slower disease progression phase of disease. Therefore, our hypothesis is that CD4+CD25+ Treg cells play a regulatory role delaying the microglia/monocyte shift from a protective (M2) to a toxic (M1) state as disease progresses and that the adoptive transfer of CD4+CD25+ Treg cells will prolong the protective M2 state and delay disease progression of mSOD1 transgenic mice. Thus, Specific Aim 1 will identify distinct activation states of microglia/monocytes at different disease phases in mSOD1G93A mice by quantitative RT-PCR, flow cytometry and immunohistochemistry using M1 and M2 markers. Specific Aim 2 will examine the interaction between different microglia/monocyte activation states and CD4+CD25+ Treg cells in vitro. Additionally, M1 and M2 phenotypes will be detected in the spinal cords and blood of Treg-depleted mSOD1G93A mice in vivo. Specific Aim 3 will determine if the adoptive transfer of CD4+CD25+ Treg cells prolongs the M2 microglial phenotype and has beneficial effects in mSOD1G93A mice. Disease progression, motoneuron loss, activation states of microglia/monocytes will be examined in the transferred mice. This project will provide in vitro and in vivo evidence that CD4+CD25+ Treg cells regulate M2 microglia/monocytes and provide neuroprotection in ALS mice. Since ALS patients seek medical attention only after disease onset, therapies directed at slowing disease progression, such as utilizing CD4+ CD25+ Treg cells, are critically needed. PUBLIC HEALTH RELEVANCE: ALS is a horrific, devastating neurodegenerative disease in which patients watch themselves deteriorate over a very short period of time, and despite extensive basic investigations, there is minimal effective therapy. Our own efforts to develop meaningful therapies have focused upon the roles of the innate and adaptive immune systems. Recently, T cells have been shown to have the ability to improve neurological function and life expectancy in ALS models - since T cells are readily accessible in ALS patients, defining the specific populations mediating neuroprotection in the ALS models is translatable into our ultimate goal of using T cell therapies in ALS patients to slow disease progression and improve their quality of life.